In a light emitting element such as an LED, a fluorescent lamp, an EL (electro-luminescence) element, and a plasma display, an outer sheath member of a luminous body is formed by a clear lens, a protecting film or a glass tube, and light is emitted to the outside (into the air) through the surface of the outer sheath member.
In general, a refractive index of this transparent outer sheath member is much greater than the refractive index of air. Therefore, when the light is emitted to the outside from the outer sheath member, reflection occurs at a boundary between the outer sheath member and the air. In some cases, according to an angle of reflection of the light, the light reflected at the boundary is not emitted from the inside to the outside of the outer sheath member, and the light is converted into heat in the end.
Further, a light emitting element such as an LED has a substrate, on which a semiconductor multilayer film including a light emitting layer is laminated to provide a semiconductor element, and the semiconductor element is packaged with resin, etc. However, since the refractive index is different between the upper-most layer of a light outlet port of the semiconductor element and the resin of the package, reflection occurs at their boundary.
When looking at the light emitting element from outside, the reflection of the light at the boundary will result in a deterioration in the luminous efficiency. Further, since the temperature of the light emitting element increases, the life duration of the light emitting element will be disadvantageously shortened. A device incorporating this light emitting element may disadvantageously suffer from adverse effects due to elevated temperature of the light emitting element.
As a counter-measure for preventing a decrease in the luminous efficiency due to the reflection at the boundary, for example, Patent Documents 1 and 2 disclose methods of providing a fine asperity structure on the boundary surface.    Patent Document 1: Japanese Laid-open Patent Publication No. 2003-174191    Patent Document 2: Japanese Laid-open Patent Publication No. 2003-209283